Function to check validity of client

Can't find any function to check if a client connection is valid (accessible and sas token valid), until after trying to upload/download something. Ideally I would like to verify my client before operating on it. Something like:
```
auto cred = std::make_shared(sas_token);
auto account = std::make_shared(ACCOUNT_NAME, cred, USE_HTTPS);
auto client = std::make_shared(account, MAX_CONCURRENCY);
bool valid = client->valid(); // I'm missing something like this
```
What do you think?